Implement buffer interface and tests

- Implement buffer_open_file/string, buffer_read, buffer_close in v0/src/buffer.c

- Add tests in v0/tests/test_buffer.c and test_buffer.txt; register tests in v0/tests/test.c

- Update v0/include.mk and Makefile

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

v0/tests/test.h

@@ -4,8 +4,7 @@
 #ifndef TEST_H
 #define TEST_H
 
-// @copilot fix the syntax. This is a typedef for any function taking a void and returning void.
-typedef Test void(void);
+typedef void (*Test)(void);
 
 /**
  * Fails a test.